Introduction of flux pinning centers in melt textured REBa2Cu3O7-x (REBCO where RE is a Rare Earth metals such as, for example, Y, Sm, Nd, etc.) is known to improve the critical current density (Jc) of such superconductive materials significantly. Approaches to obtain significant enhancements by incorporating nanometer sized particulates that act as flux pinning centers in REBCO thin films has also been recently demonstrated. For example, significant improvements in Jc have been demonstrated in the prior art in pulsed laser deposited (PLD) YBCO films with Y2BaCuO5 (Y211), Y2O3, Nd2O3, and BaZrO3 particulates.
In such PLD films, particulates are generally introduced by two prior art methods as explained hereafter. The first approach uses a single YBa2Cu3O7 (Y123) target which includes finite amounts of a second phase material. The target is prepared by blending YBCO powder with a desired amount of second phase materials and sintered them together to form a composite target of the superconductor and pinning materials. However, reactions with the pinning material and YBCO during the target preparation are possible in this approach if the pinning material is not chemically compatible with the YBCO. In addition, targets with dissimilar melting point compositions (e.g. low melting point metal+YBCO) are hard to make. Furthermore, the single composite target offers little control on the content, size, and distribution of the pinning centers through the thickness of the films formed during the pulsed laser deposition process.
The other approach uses two different targets of YBCO and the second phase material. During deposition each target is alternatively switched in a periodic fashion resulting in the introduction of island growth pining centers in a layered fashion. One disadvantage of this approach is that the second phase material particles may have to stay at high growth temperature (750-780° C.) for long time on a YBCO film during the period that the targets are switched causing opportunity for particle growth and increased extent of any reactions. Another particular disadvantage, other than the necessity of alternating between targets, is that the pinning centers generally are arranged in a lamellar fashion. This laying of the second phase particles throughout the superconductive film causes pinning centers with a more directional dependence of the critical current density (Jc). The formation of a directionally dependent critical current density (Jc) is undesirable as a random distribution of the pinning centers in the films without the layered structure is desired to avoid any preference for a given magnetic field orientation. A non-directional critical current density (Jc) is especially useful in superconducting coil applications, where the magnetic field is present at a variety of angles to the coils.